Updates writer Eleanor Ford has used a secondhand Toshiba EM925A5A-BS for about seven months now. Even with the previous life of this microwave, our pick has lived up to its reputation. “It’s never failed to do what I expect a microwave to do, heats evenly, doesn't scorch, and is significantly more quiet than any other microwave I’ve used (including my parents’),” Eleanor said. They also noted that the small size allows the microwave to sit on a shelf rather than take up valuable counter space. Eleanor also said that the only notable downside is that they find it difficult to locate the kitchen timer button.

Volume control is one of the best extra features a microwave can have, but it’s pretty rare. Some models allow you to mute the beeping, but few microwaves let you adjust the actual volume. We also prefer models that stop beeping when the oven door is opened. It’s a small perk but one that many of our testers appreciated, particularly those who find the beeping annoying.
Like most microwaves we tested, the Toshiba wasn’t great at defrosting meat. This model doesn’t beep to remind you to flip the meat halfway through heating, so if you forget, the results are pretty unappetizing. The ground beef we attempted to defrost in this Toshiba remained partially frozen in the center, while the edges were slightly cooked. For that reason, we don’t ever recommend using a microwave for defrosting meat unless you absolutely have to. It’s always best to thaw meat in the fridge or under cold running water. That said, we still think the defrost mode is great for quickly thawing frozen bread or bagels.

There are, however, a few cases where people have been exposed to direct microwave radiation, either from appliance malfunction or deliberate action.[67][68] The general effect of this exposure will be physical burns to the body, as human tissue, particularly the outer fat and muscle layers, has similar composition to some foods that are typically cooked in microwave ovens and so experiences similar dielectric heating effects when exposed to microwave electromagnetic radiation.
In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.[10][11] To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October 1945, Raytheon filed a United States patent application for Spencer's microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing.[12]
The lower temperature of cooking (the boiling point of water) is a significant safety benefit compared to baking in the oven or frying, because it eliminates the formation of tars and char, which are carcinogenic.[49] Microwave radiation also penetrates deeper than direct heat, so that the food is heated by its own internal water content. In contrast, direct heat can burn the surface while the inside is still cold. Pre-heating the food in a microwave oven before putting it into the grill or pan reduces the time needed to heat up the food and reduces the formation of carcinogenic char. Unlike frying and baking, microwaving does not produce acrylamide in potatoes,[50] however unlike deep-frying, it is of only limited effectiveness in reducing glycoalkaloid (i.e., solanine) levels.[51] Acrylamide has been found in other microwaved products like popcorn.
The exploitation of high-frequency radio waves for heating substances was made possible by the development of vacuum tube radio transmitters around 1920. By 1930 the application of short waves to heat human tissue had developed into the medical therapy of diathermy. At the 1933 Chicago World's Fair, Westinghouse demonstrated the cooking of foods between two metal plates attached to a 10 kW, 60 MHz shortwave transmitter.[3] The Westinghouse team, led by I. F. Mouromtseff, found that foods like steaks and potatoes could be cooked in minutes.